The present invention relates to a connecting rod bearing for internal combustion engines, which consists of a pair of semicircular bearings, which rotatably supports a crankpin which connects a connecting rod and a crank shaft, and in which lubricant oil fed to an inner surface of a main bearing supporting the crank shaft is fed to an inner surface of the connecting rod bearing through an internal lubricant-oil path formed in the crank shaft.
A crank shaft of an internal combustion engine is supported in a lower portion of a cylinder block of the internal combustion engine at a journal section thereof through a main bearing consisting of a pair of semicircular bearings. In the main bearing, lubricant oil discharged from an oil pump is transferred, through an oil gallery formed in the cylinder block wall and a through hole formed in the wall of the main bearing, to a lubricant groove formed along the inner surface of the main bearing. In addition, a first lubricant-oil path is radially formed in the crank journal section, openings of both ends of the first lubricant-oil path is connected to the lubricant groove, a second lubricant-oil path is formed so as to branch off from the radial first lubricant-oil path in the crank journal section to pass through a crank arm, and the second lubricant-oil path is fluid communication with a third lubricant-oil path radially formed in a crankpin. Thus, the lubricant oil, which is fed from the oil gallery in the cylinder block wall via the through hole formed in the wall of the main bearing into the lubricant groove formed along the inner surface of the main bearing, flows in the first to third flow lubricant-oil path and be supplied between the crankpin and a sliding surface of the connecting rod bearing from an outlet port of an end portion of the third lubricant-oil path.
The lubricant oil, which is fed from the cylinder block of the engine through the crank journal section to the connecting rod bearing, might accompany foreign substances existing in the respective lubricant-oil path. If such foreign substances accompanied with the lubricant oil is fed between the crankpin and the sliding surface of the connecting rod bearing, there is a risk that they damage the sliding surface of the connecting rod bearing. The foreign substances entered between the crankpin and the sliding surface of the connecting rod bearing are required to be quickly discharged from the sliding surface to outside.
As a countermeasure against the foreign substances admixed in the lubricant oil, there has been a proposal that a circumferential lubricant groove is provided on an inner surface of one semicircular bearing of a main bearing, supporting a crank journal section, throughout an overall circumferential length thereof, the main bearing consisting of a pair of semicircular bearings, which semicircular bearing has a through hole receiving a lubricant oil supply directly from an oil gallery in a cylinder block wall, whereby discharging the foreign substances accompanied with the lubricant oil. In the case where this idea to a connecting rod bearing, it was found by a test that a foreign substances discharge effect is not obtainable, and such a way is rather counterproductive, because the foreign substances not only stay in the circumferential lubricant groove formed on an overall circumferential inner surface of one semicircular bearing of the connecting rod bearing but also the foreign substances are dispersed throughout a sliding surface of the bearing resulting in that the connecting rod bearing is liable to be damaged.
This is because in general a housing holding a connecting rod bearing is deformed largely during operation of an internal combustion engine, so that a clearance between a crankpin and the connecting rod bearing is larger than a clearance between the crank journal section and the main bearing, and the foreign substances staying in the circumferential lubricant groove is liable to be spread throughout the sliding surface of the bearing including a primary load bearing section which is a circumferential center region of the semicircular bearing whereby the connecting rod bearing suffers increased damages as compared with a conventional connecting rod bearing without such a circumferential lubricant groove. This was confirmed by a test    Prior Art Publication 1: JP-A-8-277831    Prior Art Publication 2. JP-A-2005-69283